1. Field of Invention
The invention concerns a bag-making device for cross base bags.
2. Description of the Prior Art
These devices are known and are acknowledged, e.g., in the document DE 198 05 321 C1. In more recent times, there has been an increasing demand for cross base bags with small volumes. Cross base bags can have a small volume by means of a smaller base middle measurement. However, the manufacture of bags with smaller base middle measurement requires the implementation of extensive constructive changes in the means of production, primarily in bag making devices. Since the bags are conveyed at right angles to the principal axis of the tube through the working station of the bag-making device, both the working stations and also the conveyor system have to be formed in a narrower configuration than they have been previously.
One of the necessary measures is the use of narrower conveyor belts for conveying the bags through the working stations of the bag-making device. However, the conveyor belts are exposed to a considerable amount of tensile stress and run the risk of being stretched. This tendency increases with the decreasing breadth of the conveyor belt. The result of changing the length of the conveyor belt in the operation, however, is that the bag positions in the working stations no longer correctly align with the rotary motions of the tool rollers. The tools run through their machining position when the bag is not yet or is no longer located at the right place, and the related working step is executed inaccurately. As a result, the normal fabrication tolerances of the bags can be exceeded, resulting in serious quality defects in the bags, e.g., leakiness and lack of durability. These consequences are highly undesirable.
For these reasons the use of conveyor belts is recommended that have at least components made of tensile-stressable material such as steel. Typically these components of the belt are coated with a more elastic and softer material that prevents the conveyed items from being damaged. In this context the so-called cable cord belts may be employed that contain steel in their core and are usually coated with rubber.
Unfortunately conveyor belts of the above-described kind have fabrication tolerances that can be exceeded when the belt is stretched. The result of these fabrication tolerances is once again imprecisions in the positioning of the bags in the machining positions and thus in the fabrication tolerances of the bags.